Electrosurgical tools have been used for a number of years to cut and shape tissue at the surgical sites to which these tools are applied. A typical electrosurgical tool has an elongated shaft, sometimes called a “probe,” with a handle at one end and a tip at the opposed end. One type of electrode surgical tool available to surgeons is referred to as a bipolar electrosurgical tool. An active electrode is fitted into the tip of this tool. The shaft of the bipolar electrosurgical tool functions as the return or reference electrode. The tool is applied to a surgical site at which there is a saline solution, a conductive fluid. A voltage is applied at a very high frequency, 50 k Hz to 10 M Hz, from the active electrode to the adjacent end of the shaft. This signal flows through, arcs through, the saline solution and the body tissue against which the tip is applied. When the signal is at a relatively low power, typically under 40 Watts, the signal can coagulate fluid such as blood to seal the tissue closed. When the signal is at a relatively high power, typically 20 Watts or more, it vaporizes the tissue to which it is applied so as to ablate, remove, the tissue. The overlap in the power ranges between the coagulation and ablation modes of operation is due to the fact that, for a given power setting, whether or not a particular electrode coagulates or ablates tissue is also a factor of the size and shape of the head of the electrode. Often, when an electrosurgical tool is used to ablate tissue, it is considered to be operated in the “cutting” mode.
Many currently available electrosurgical tools are designed so that mounted to the handles are switches for regulating the on/off state of the tool and the mode in which the tool is operated. The mounting of these switches to the tool handle makes it possible for the surgeon to, with a single hand, control both the position of the tool and the operation of the tool. The switches are typically mounted to the tool handle in liquid-tight seal assemblies. This mounting is necessary to prevent the conductive liquid that is often present in a surgical environment from entering the handle and shorting out any electrical components therein.
Presently available electrosurgical tools work reasonably well for the purposes for which they are designed. However, there are still some limitations associated with the currently available tools. Some of these limitations are due to the fact that, when an electrosurgical tool is operated in the ablation mode, bubbles form on the surface of the active electrode. One reason these bubbles form is that the electrical energy discharged by the electrode heats the conductive saline solution that surrounds the electrode. The heating of this solution causes it to vaporize and form bubbles. Initially, when relatively low levels of heat are present, the fluid immediately adjacent the surface of the electrode is subjected to thin film boiling and transitional boiling. In this type of vaporization, relatively small bubbles of gaseous state solution form.
However, when additional thermal or electromagnetic energy is radiated from the surface of the active electrode, the adjacent saline solution is subjected to rapid nucleate boiling. During nucleate boiling, relatively large bubbles of vaporized solution form on the surface of the electrode. These bubbles are sometimes referred to as gas pockets. Moreover, during some high powered cutting modes of operation, the electrical current applied to the solution and surrounding tissue causes electrochemical processes to occur in this tissue and liquid. These electrochemical processes produce gaseous state products that contribute the formation of large bubbles and the gas pockets.
At a minimum, these bubbles are a nuisance. The presence of these bubbles interferes with the surgeon's view of the surgical site. This is especially a problem when the electrosurgical tool is employed in an endoscopic surgical procedure. In an endoscopic procedure, the electrosurgical tool is applied to the surgical site through a small opening formed in the patient's body known as a portal. The surgeon views the surgical site through an endoscope that is directed to the surgical site through another portal. An advantage of an endoscopic surgical procedure in comparison to a conventional surgical procedure is that it requires less of the patient's body to be opened up in order to gain access to the surgical site. However, when a conventional electrosurgical tool is employed in an endoscopic surgical procedure, the bubbles generated in the relatively small confines of the space of the surgical site can significantly block the surgeon's view of the site.
Moreover, these bubbles are electrically and thermally insulating. The large bubbles that form gas pockets during high powered cutting can inhibit the flow of new solution that rewets the electrode. Consequently, the bubbles reduce the extent to which current can arc through the tissue that is to be ablated. Sometimes, these bubbles significantly reduce current flow through the tissue. The current flow stays in the reduced state until the bubbles collapse or move away and the saline solution or body fluid flows back into the space between the electrode and the shaft. Thus, sometimes when a presently available electrosurgical tool is actuated, the current only flows in a pulse pattern through the tissue to be ablated.
Moreover, many current electrosurgical tools are provided with wire wound electrodes. It is difficult to form wire wound electrodes so that they have heads with shapes that are especially useful for performing electrosurgical procedures.
Providing a seal around the handle switches can significantly add to the overall cost and assembly of the tool.
Also, sometimes, even with the best seals, there may be liquid leakage into the handle of an electrosurgical tool. This leakage, if not promptly detected, at a minimum, can lead to the degradation of the tool performance. In a worse case scenario, this leakage can cause a conductive path to develop along the outer surface of the handle. If this occurs, the personnel handling the tool may be subjected to electrical shock.
Still another method by which an electrosurgical tool is employed to shape, remove very selected amounts of tissue is by a capsulary shrinkage procedure. In a capsulary shrinkage procedure, the cells forming soft tissue are desiccated, reduced in size. In this type of procedure, as a result of the heating of the active electrode, there is a conductive transfer of the heat from the electrode to the location at which the capsulary shrinkage of tissue is to occur. The thermal energy applied to the site causes the cells forming the tissue at the site to undergo capsulary shrinkage. This process is referred to as a thermally capsulary shrinkage procedure.
In a presently available electrosurgical tool, internal to the tip or distal end of the shaft there may be a small thermistor or other temperature-sensitive transducer. This transducer monitors the temperature of the active electrode to inferentially provide an indication of the temperature of the surgical site. This temperature data is very important because there is a limited temperature range to which tissue can be heated in order to foster its shrinkage without causing damage to the tissue. More particularly thermal capsulary shrinkage of tissue is best performed by heating the tissue to a temperature between 60 and 70° C. If the tissue is heated to a temperature above this range, it may suffer damage. More particularly, the cells forming the tissue may die if heated to a temperature above 70° C. Therefore, when a thermal capsulary procedure is now performed, the temperature of the active electrode is monitored in order to regulate the application of an energization voltage to the electrode. Specifically, the application of the energization voltage to the active electrode is controlled to maintain its temperature within the range at which the thermal capsulary shrinkage process can best occur and to prevent it from rising to level at which cell death or damage can occur.
One disadvantage of the presently available electrosurgical tools is that the transducer internal to the tool only measures the temperature of the adjacent active electrode. This temperature measurement is only an approximate measurement of the temperature at the site to which the electrode is applied. Given the presence of fluids and other material around the active electrode and, more particularly, between the transducer and the surgical site, this measurement may not accurately represent the temperature at the site to which the electrode is applied.
Still another disadvantage associated with the currently available electrosurgical tool relates to the fact that often an AC signal is used to energize the active electrode. This signal generates stray electromagnetic waves. These electromagnetic waves interfere with the generation of the output signal generated by the transducer. Accordingly, it is now common practice to energize an electrosurgical tool in an on/off/on/off pulsed pattern. During time periods when the energization signal is pulsed on, the transducer signal is not employed as a feedback signal since it is adversely affected by the stray electromagnetic waves. Only during the time periods at which the energization signal is pulsed off, and the transducer signal is relatively noise free, is the signal then employed by the downline components as the input signal for regulating the application of energy to the active electrode.
One disadvantage of this mechanism is that the pulsing of current through the active electrode may stress the material from which the electrode is formed. Another disadvantage of this process is that the pulsing causes the thermal energy generated by the electrode to itself be generated in an on/off/on/off pattern. The cyclic generation of this heat can cause it to be unevenly applied to the surgical site. The uneven application of this heat can in turn both make it difficult to control the application of heat and lengthen the time it takes to perform the desired thermal capsulary shrinkage procedure.